I just read through the whole Complaint. I don't know the whole history of the animosity between ME and EM (ironic that their initials are mirror images -- like arch enemies in a comic book or something). I am relatively new to this board and to Tesla in general, and only really got interested when I heard the Model S was on its way. So take what I write below as coming from a complete outsider solely analyzing this from a legal practitioner's point of view -- I have no horse in this race and don't know who is the good guy or bad guy in this dispute.
In any case, solely from a legal point of view ME has a pretty weak case based on the Complaint. Obviously, he and EM don't like each other much, but there's nothing unlawful or actionable in saying things like, "Martin Eberhad is the worst person I've ever met or worked with", which EM allegedly said at one point. Most or all of what EM says about ME is opinion, not knowingly false facts, and that is the standard for a defamation claim.
ME's claim about the "Founder" issue is also weak because most or all of his examples are situations where someone else calls EM the "founder" of TM, and he faults EM for failing to correct them. I mean, if it was EM's (or anyone's) responsibility to correct every false bit of information that the media says, he'd never stop issuing corrections! I know of no case where a court would allow a claim of defamation based on statements by others that weren't corrected by the defendant -- that's too high a burden to place on people. And even if ME were right about the Founder issue, his assertion that because EM wanted to be known as a "Founder" at PayPal seems a bit attenuated, especially because they didn't put a specific dollar value on it.
I think ME's strongest argument is on his car. That's a pretty weird story, and I could see a court giving ME some compensation for the fact that EM may have negligently allowed ME's car to get in an accident before it was ever delivered to him. ME, though, will have a very tough time proving that his car is/was worth "millions", as he claims.
The good news and bottom line (from my perspective) is that this isn't going to take down Tesla, although it clearly could be a distraction and diversion. As someone who does this for a living, I tell plaintiffs and defendants that the only people who win in a lawsuit are the lawyers -- I don't know the whole history here, but it's clearly quite acrimonious, and tragic that their relationship devolved to this point. The one thing I am certain of is that neither EM nor ME will be completely satisfied with the result and it's going to waste a lot of everyone's time.